Sign me up for #1 as well - the talk of a UA/US merger had me going overboard.
You have to feel a bit bad for US - caught up as the stalking horse in this deal, now too ugly for anyone. Makes one wonder what the impact is going to be on their long term survival.
I don't think that US officially backing away takes the heat off CO to move ahead with the merger. Parker stated publicly in the walk away press release that they intend to be active participants in any industry consolidation. I think CO is smart enough to know that US would gladly take up talks with UA again...probably in a heartbeat.